Photopolymerizable inkjet inks containing (meth)acrylic esters, and photopolymerizable inkjet inks containing (meth)acrylic esters and vinyl ethers in combination have been widely known (see, for example, PTL 1).
However, many of the monomers used in such conventional photopolymerizable inkjet inks have toxicity. In particular, most of (meth)acrylic esters, which are inexpensive and easily procured, exhibit high skin sensitization, causing allergy on a skin brought into contact with them, but conventional art has not provided any solution to this problem.
Reducing viscosity of a photopolymerizable inkjet ink may be easily achieved by adding a diluting solvent, but the solvent released into the atmosphere by volatilization is not desirable in view of environmental impact.
A photopolymerizable water-based inkjet ink blended with water is heretofore known, but penetration drying on an impermeable substrate is not expected as described later. As a result, it requires a step of evaporating water for faster and more efficient process, requiring installation of heat source and so on, which is not desirable in view of energy conservation.
For further improvement of the performance of the photopolymerizable inkjet ink, it has been desired to improve strength of a cured film thereof by increasing durability against abrasion and to reduce viscosity thereof to so as not to interfere with inkjet discharge despite being thickened due to blending with various materials such as pigments and additives.